1. Field of the Invention
The present invention relates to a diplexer, and more particularly, to a compact lumped-distributed diplexer implemented on a printed circuit board for a wireless communication device.
2. Description of the Prior Art
In radio frequency front end circuit, a diplexer is an important high frequency component having three signal ends of two-to-one or one-to-two, for separating a mixed signal received from an antenna into different bandwidth signals, or sending a signal from a signal end to the signal end coupled to the antenna without leakage. Generally, the diplexer needs good isolation to avoid the interference when the two signal ends transmit different frequency signals.
A conventional diplexer is composed of a low-pass filter and a high-pass filter (or a band-pass filter) to separate different frequencies. Please refer to FIG. 1, which is a schematic diagram of a diplexer 10 according to the prior art. The diplexer 10 includes signal ends S1, S2 and S3, a low-pass filter LPF, and a high-pass filter HPF. The signal end S1 is coupled to an antenna 12, and used for receiving and transmitting a bandwidth signal LB and HB corresponding to a low frequency band and high frequency band respectively. Take the diplexer 10 operated in a receiving link as an example, after the signal end S1 receives the bandwidth signals LB and HB, the low-pass filter LPF filters out the bandwidth signal HB, and outputs the bandwidth signal LB to the signal end S2. The high-pass filter HPF filters out the bandwidth signal LB, and outputs the bandwidth signal HB to the signal end S3.
However, if the diplexer 10 is implemented on a printed circuit board, the circuit of the design occupies a serious area. Therefore, an application of a communication product now, such as a wireless access point device, a wireless router, or a wireless network card, the diplexer 10 is difficult to be integrated into a circuit system.